[UPDATE: Here’s a video explaining how subduction faults generate such potent earthquakes and tsunamis, created by Steven Ward, a geophysicist at the University of California, Santa Cruz:]

The Pacific “ring of fire” doesn’t stop at the equator. While my print story and post on quake threats last week focused on the seismic peril facing millions of poor people living in fast-growing cities in quake zones, there are plenty of prosperous places that have not adequately responded to their exposure to enormous, and inevitable, earthquake risk.

“The release of pressure between two overlapping tectonic plates along the subduction zone regularly generates massive 9.0 magnitude earthquakes –- including five over the last 1,400 years. The last ‘Big One’ was 309 years ago. We are in a geologic time when we can expect another ‘Big One,’ either in our lives or those of our children. Prudence dictates that we overcome our human tendencies to ignore this inevitability.”

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By 2050 or so, the human population is expected to pass nine billion. Those billions will be seeking food, water and other resources on a planet where humans are already shaping climate and the web of life. Dot Earth was created by Andrew Revkin in October 2007 -- in part with support from a John Simon Guggenheim Fellowship -- to explore ways to balance human needs and the planet's limits.